1. Field of the Invention
This invention relates to a control system for an automatic vehicle transmission.
2. Description of the Related Art
In a typical prior-art control system for automatic vehicle transmissions, the gear ratio of the automatic transmissions is determined by retrieving a predetermined shift program (map) using the vehicle speed and throttle opening as address data.
Moreover, Japanese Laid-Open Patent Application No. Hei 5 (1993)-71625, for example, teaches a control system for automatic vehicle transmission, in which a parameter indicative of the running resistance, more specifically a parameter indicative of the downgrade or upgrade of vehicle running is determined based on the vehicle speed and throttle opening to select one from among a plurality of shift programs (shift characteristics) for upgrade, downgrade, etc., and the gear ratio is determined by retrieving the selected program based upon the vehicle speed and throttle opening such that the gear ratio is appropriate both in upgrade or downgrade vehicle running.
However, if the gear ratio is solely determined and controlled by retrieving a single shift program or one selected from among a plurality of shift programs, whichever it may be, the driveability, i.e., the performance of vehicle running or vehicle driving experienced by the vehicle operator may sometimes be degraded depending upon the road on which the vehicle is traveling.
In order to solve this problem, Japanese Laid-Open Patent Application No. Hei 7 (1995)-286664 teaches determining whether the vehicle runs on a traffic jammed or crowed road, and whether the vehicle runs on an upgrade road. In the prior art control, when it is determined that the vehicle runs on a traffic jammed road, but is not running on an upgrade road, the shift to the 1st gear is inhibited, while when it is determined that the vehicle runs on a traffic jammed and upgrade road, the gear ratio is controlled based on the shift program for upgrade. When the vehicle is determined to be running not on a traffic jammed road, but on an upgrade road, the gear ratio is controlled in response to the determination of upgrade.
Similarly, Japanese Laid-Open Patent Application No. Hei 5 (1993)-280624 discloses making fuzzy reasoning based on the engine load and the jerk of vehicle to determine the degree of certainty, i.e., the degree to which it is believed that the road on which the vehicle is travelling is, in fact, a winding road. When it is determined that the vehicle runs on such a road, the gear ratio is controlled to a lower gear to generate the engine braking effect.
However, although these prior art techniques propose determining whether the vehicle runs on a traffic jammed road, an upgrade road or a winding road and controlling the gear ratio based on the determination, they do not teach determining whether the vehicle runs on a relatively narrow road such as an alley or an expressway under traffic jam conditions and controlling the shift control based on the determination.
When the vehicle runs on a relatively narrow road such as an alley, the vehicle driving should be conducted paying a careful attention to all of the surroundings, and the operation of the accelerator pedal and the brake pedal increases. If the gears are shifted frequently in response to the accelerator pedal operation, this will cause shift hunting (the hunting in control) to occur and degrading the driveability.
Moreover, when the vehicle runs at a low speed on a traffic jammed expressway, if the gear is unnecessarily kept to a lower gear, the engine braking is effected such that the vehicle operator feels the frequency of the engine braking effect too much, thereby similarly degrading the driveability.
Aside from the above, the range of navigation systems extends to embrace everything from simple orientation aids to guidance systems featuring automatic route determination. The navigation system has a road-map memory stored in a CD-ROM or the like, and detects the instantaneous vehicle position by, for example, the GPS (Global Positioning System) satellite position system, and provides directional information on a road map including the detected instantaneous vehicle position.
Since the use of such navigation information enables the recognition or prediction of the details of the road on which the vehicle is traveling, it will be desirable to determine the aforesaid running conditions based on the navigation information and other parameters including average vehicle speed and to conduct gear-shift control in response to the determined running conditions such that the driveability is improved.